參數(shù)資料
型號: LTC1402I
廠商: Linear Technology Corporation
英文描述: 10-Bit Bus-Interface D-Type Latches With 3-State Outputs 24-PDIP 0 to 70
中文描述: 串行12位,2.2Msps采樣ADC,帶有關(guān)斷
文件頁數(shù): 15/20頁
文件大小: 251K
代理商: LTC1402I
15
LTC1402
APPLICATIO
S I
N
FOR
ATIO
U
The SCK and CONV inputs control the power-down modes
(see Timing Diagrams). Two rising edges at CONV, with-
out any intervening rising edges at SCK, put the LTC1402
in Nap mode and the power drain drops from 90mW to
15mW. The internal reference remains powered in Nap
mode. One or more rising edges at SCK wake up the
LTC1402 for service very quickly, and CONV can start an
accurate conversion within a clock cycle. Four rising edges
at CONV, without any intervening rising edges at SCK, put
the LTC1402 in Sleep mode and the power drain drops
from 90mW to 10
μ
W. One or more rising edges at SCK
wake up the LTC1402 for operation. The internal reference
(V
REF
) takes 2ms to slew and settle with a 10
μ
F load, and
the REFREADY bit in the D
OUT
stream takes an additional
10ms to go high after the reference output Pin 5 (V
REF
) has
finished slewing. Figure 11 shows the power consumption
versus the conversion rate. Note that, for slower conver-
sion rates, the Nap and Sleep modes can be used for sub-
stantial reductions in power consumption.
W
U
Figure 11. Power Consumption vs Sample Rate
in Normal Mode, Nap Mode and Sleep Mode
CONV at Pin 16
The rising edge of CONV starts a conversion but subse-
quent rising edges at CONV, during the following 14 SCK
cycles of conversion, are ignored by the LTC1402. The
duty cycle of CONV can be arbitrarily chosen to be used as
a frame sync signal for the processor serial port. A simple
approach to generate CONV is to create a pulse that is one
SCK wide to drive the LTC1402 and then buffer this signal
with the appropriate number of inverters to drive the frame
sync input of the processor serial port. It is good practice
to drive the LTC1402 CONV input first to avoid digital noise
interference during the sample-to-hold transition triggered
by CONV at the start of conversion. Another point to con-
sider is the level of jitter in the CONV signal if the input
signals have fast transients or sinewaves. Some proces-
sors can be programmed to generate a convenient frame
sync pulse at their serial port, but often this signal is de-
rived from a jittery processor phase locked loop clock
multiplier. This is true even if a low jitter crystal clock is the
reference for the processor clock multiplier.
SCK at Pin 15
The rising edge of SCK advances the conversion process
and also udpates each bit in the D
OUT
data stream. After
CONV rises, the second rising edge of SCK sends out the
REFREADY bit. Subsequent edges send out the 12 data
bits, with the MSB sent first. A simple approach is to
generate SCK to drive the LTC1402 and then buffer this
signal with the appropriate number of inverters to drive the
serial clock input of the processor serial port. The rising
edge of SCK is guaranteed to coincide with stable data at
D
OUT
. It is good practice to drive the LTC1402 SCK input
first to avoid digital noise interference during the internal
bit comparison decision by the internal high speed com-
parator. Unlike the CONV input, the SCK input is not
sensitive to jitter because the input signal is already
sampled and held constant.
D
OUT
at Pin 10
Upon power-up, the D
OUT
output is automatically reset to
the high impedance state. The D
OUT
output remains in high
impedance until a new conversion is started. D
OUT
sends
out 13 bits in the output data stream after the second rising
edge of SCK after the start of conversion with the rising
SAMPLE RATE (MHz)
0.01
0.1
S
10
1
0.01
0.1
1
1402 F11
0.001
100
10
V
DD
CURRENT
DUAL
±
5V
V
DD
CURRENT
SINGLE 5V
V
CURRENT
DUAL
±
5V
V
SS
CURRENT
SINGLE 5V
V
CURRENT
SLEEP MODE
V
CURRENT
NAP MODE
DIGITAL INTERFACE
The LTC1402 has a 3-wire SPI (Serial Protocol Interface)
interface. The SCK and CONV inputs and D
OUT
output
implement this interface. The SCK and CONV inputs are TTL
compatible and also accept swings from 3V or 5V logic. The
amplitude of D
OUT
can easily produce 5V logic or 3V logic
swings by tying the independent output supply Pin 11
(OV
DD
) to the same supply as system logic. A detailed
description of the three serial port signals follows.
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